Implement `sum_root_to_leaf_numbers(values)` for a binary tree serialized as a zero-based heap array. For an existing node at index `i`, its children are at `2 * i + 1` and `2 * i + 2`. A `null` slot means no node, and an existing node never appears below a missing parent. Every existing value is a decimal digit from `0` through `9`. Each root-to-leaf path forms a number by concatenating its digits from root to leaf. Return the sum of all such numbers. A leaf has no existing left or right child, and an empty serialization returns `0`. For example, a root `1` with children `2` and `3` forms `12` and `13`, so the result is `25`. ```hint Carry the prefix numerically When visiting digit `d` with accumulated prefix `p`, the new prefix is `p * 10 + d`. ``` ```hint Add only at leaves Internal prefixes are not complete path numbers. Contribute the accumulated value only when both children are absent. ``` ### Discussion Extensions - How would an iterative depth-first traversal avoid recursion depth limits on a very deep tree? - What is the time complexity in terms of nodes and the auxiliary space in terms of tree height?